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 a页面和b页面同域，a访问c页面的数据
 a给c传一个hash指，c收到hash后，c把hash传给b，b再将收到的结果放到a的hash中
 <iframe src="http://localhost:4000/hash/c.html#iloveyou"></iframe>
 <script>
   window.onhashchange = function(e) {
    console.log(e); 
    console.log(location.hash);
   }
 </script>
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